Vacuum breakers are used in fluid supply systems and, in particular, in potable water systems to eliminate or lower the probability of back-siphonage at the discharge side of such systems. Vacuum breakers are particularly useful in conjunction with laboratory faucets and valves that are part of a potable water system to prevent contaminated water from being siphoned back into the water system. In many laboratory procedures, one end of a flexible hose or tubing is attached to an outlet fitting of the faucet or valve, such as a serrated nozzle, while the other free end rests in a sink. The concern is that in the event of a loss of water pressure--due, for example, to a pipe breaking or a sudden large demand in the water lines elsewhere in the system--a siphon will be created in the faucet and contaminants in the sink will be drawn up through the hose or tubing and into the potable water system. A vacuum breaker is employed to prevent the back-siphonage from occurring. In a typical application, the vacuum breaker is an integral part of the gooseneck of a faucet and contains some type of valve means. In another typical application, the vacuum breaker is installed in the piping within a fume hood or cabinet between a water valve and an outlet fitting. In either application, when the faucet or valve is opened the vacuum breaker permits water to flow therethrough. When there is a loss of water pressure, however, the vacuum breaker closes off the upstream line and permits air to enter the downstream line to break any vacuum created.
One problem presented by vacuum breakers of the prior art occurs during many common laboratory procedures that require low water flow through the gooseneck. Under low flow conditions, vacuum breakers tend to leak out the air vents. One reason for the occurrence of leaking is that many vacuum breakers contain an internal float valve body which is not capable of maintaining proper seating over abroad range of flow rates, either because the float valve body is not sufficiently buoyant or is permitted excessive freedom of movability. Buildup of calcium or mineral deposits and other types of fouling of the float valve body can exacerbate this problem.
In the prior art, hollow float valve bodies have been constructed by threading two or more components together. In such float valve bodies the integrity of the seal at the threads, or the tightness of the threaded connection, has never been ensured, even where gaskets or other seals are employed to protect the threads. Both the threads and their seals are subject over time to degradation, fouling, dilation and expansion under different flow conditions or fluid temperatures. The risk of occurrence of such problems increases especially where the pressure within the hollow float valve body differs from the pressure surrounding the valve body. Air contained within the valve body, which contributes to its buoyancy, may escape through the spaces between the mated threads and may be replaced with water seeping into the valve body, thereby weighing the valve body down and severely reducing its buoyancy.
In an attempt to restrict the degree of movement of float valve bodies and maintain proper seating, vacuum breakers of the prior art have been provided with internal tubular members in which the float valve bodies are disposed. One example of such a vacuum breaker is an embodiment disclosed in U.S. Pat. No. 2,814,304, issued to Sloan. The valve body disclosed in Sloan is provided with a plurality of ribs or wings that extend radially outward from the valve body toward the tubular member. This configuration unnecessarily adds complexity to the vacuum breaker, increases the weight of the valve body, and escalates assembly and component cost. It also presents additional surfaces prone to oxidation, fouling by deposition of calcium, scale and other impurities, as well as other modes of degradation. In addition, the threads of the valve body in Sloan remain submerged in a volume of water during operation of the vacuum breaker such that the threads are especially prone to corrosion, fouling, and leaking. Because the air and water seats of this vacuum also remain submerged, an acceptable seal cannot be achieved unless water between the valve body and seat is completely displaced.
Finally, any air pocket retained within the valve body disclosed in Sloan is necessarily located above the air chamber seat, the flange of the valve body, and the rubber ring and slip ring which form the seal between the seat and the flange. Hence, the source of buoyancy of the valve body is positioned above the water level within the vacuum breaker. This configuration contributes to the inferiority of the seal because the valve body must be pulled rather than pushed upward, such that the action of the water flowing through the vacuum breaker is less effective in maintaining a good seal.
The present invention is provided to solve these as well as other problems in the prior art.